Laser absorption spectroscopy in the vacuum ultraviolet range (VUV-LAS) has been applied for the quantitative measurement of light atomic species and halogen atoms, which are of importance in various plasma processing technologies. So far, measurements of F and C atoms have been made with this method. For the generation of a VUV laser, a two-photon resonance four-wave mixing method has been used in the sum frequency generation scheme or difference frequency generation scheme. Wavelength tunability is essential when the background absorption exists due to the parent molecules and other species produced in plasmas. The absolute density of target atoms can be derived from the integral over the line profile converted into the absorption coefficient. Since the VUV-LAS measurement can yield only the values averaged over the line-of-sight, some complementary methods such as two-photon absorption laser induced fluorescence (TALIF) and optical emission actinometry are used for the spatial resolution. Examples of experimental data are given for F and C (VUV-LAS) and for O, N and H (TALIF) with a brief discussion.
Plasma Sources Science Technology
- Pub Date:
- August 2002